Method of and apparatus for electrostatic recording



March 30, 1965 R. J. DUNLAVEY METHOD OF AND APPARATUS FOR ELECTROSTATIC RECORDING Filed Dec. 27, 1960 3 Sheets-Sheet 1 INFORMATION 25- AND TIMING PULSES DlGiTAL #38 SWITCHING MEANs 20w ELECTROSTATIC RECORDING MECHANISM PERMANENT IMAGE PRODUCING 28 STATION DEVELOPMENT E MECHANISM 30/ FUSER FIG. I

INvENToR ROBERT J. DUN L AVEY ATTORNEY March 30, 1965 R. J. DUNLAVEY METHOD OF AND APPARATUS FOR ELECTROSTATIC RECORDING Filed Dec. 27, 1960 3 Sheets-Sheet 2 INPUT FROM MAGNETIC TAPE LINE SELECTION MATRIX REVOLUTION COUNTER CHARACTER REGISTER COMPARISON CIRCUIT VOLTAGE AMPLIFIERS CHARACTER COUNTER ELECTRODES RECORDING WEB MAGNETIC SPOTS (ONE PER CHARACTER) MAGNETIC READING HEADS AND AMPLIFIERS FIG.

INVEN TOR ROBERT J. DUNLAVEY BY Q ATTOR March 30, 1965 R. J. DUNLAVEY 3,175,307

METHOD OF AND APPARATUS FOR ELECTROSTATIC RECORDING Filed Dec. 27, 1960 3 Sheets-Sheet 3 RECORDING WEB CHARACTER DRUM DEVELOPING MECHANISM FIG. 3

FIG. 4

53 53 25 CHARACTER ELECTRODE 7| rllllllllillllllllll, u nun. RECORDING WEB mm B F 1 7O VIII/II.

WEI-LYING ELECTRODE 55 RL Rs CHARACTER ELECTRODE- I c I I r-BACKING ELECTRODEW PRINT-THROUGH CONVENTIONAL FIG. 5

INVENTOR ROBERT J. DUNLAVEY ATTORNE United States Patent 3,176,3fl7 METHUD OF AND APPARATUS FOR ELEQTRG- STATIC RECGRDING Robert J. Dunlavey, Palatine, Ill., assignor to Teletype Corporation, Skokie, 11]., a corporation of Delaware Filed Dec. 27, 196i), er. No. 78,391 19 Claims. (Cl. Mitt-74) This invention relates to electrostatic recording and reproduction of images.

In recent years there have been developed various types of electronic machines such as digital computers, accounting and tabulating machines, teletypewriter machines and the like which produce information at high rates of speed. Ordinary mechanical recording devices are too slow and are too cumbersome to handle the outputs involved at the operational speeds of these devices. Accordingly, there have come into being techniques and devices to record as electrostatic images the information developed by these high speed devices. The electrostatic images are made visible by developing with powered or inked materials and the visible image is generally fused or dried to make the output information permanent.

This class of read-out device has developed in a number of different forms, :and generally the choice of which form will be employed is dependent upon the type of output information to be recorded and the rate of speed of transmission desired. The choice also may depend upon the type of input to be employed as well as the type of information to be reproduced at the output point.

These various known systems in general involve positioning a recording web, generally of insulating material, at a slight distance from one of 'a number of possible recording heads. An electric bias pulse is then applied between the recording Web and generally through the recording web to result in the deposition of an electrostatic charge pattern on the recording web. The web is then generally moved to a new point and developed, thus making the charge pattern visible and the information available for use.

Now according to this invention, it has been found that images of better quality and better resolution are produced when a particular recording web comprising an insulating layer overlying a resistive layer is positioned with the resistive layer facing and preferably in physical contact with the recording head, a spaced electrode is positioned on the opposite side of the recording web and the image is developed on the insulating layer. This arrangement results in improved uniformity in images pro duced and in uniformity of developer density throughout images and from image to image. Also, an improvement in reliability of printing is apparent.

It is therefore an object of the present invention to provide improved electrostatic recording techniques and apparatus.

It is another object of this invention to devise novel and improved methods of electrostatic printing.

It is a further object of this invention to improve high speed recording devices of the read-out type.

It is a further object of this invention to provide a novel recording device for high speed print-out of information in which a resistive surface of a recording web bearing an insulating surface layer is positioned against a recording head and in which the insulating surface is spaced from an electrode at the point of electrostatic image formation on the recording web and in which developable charge patterns are formed on the insulating surface layer.

For a better understanding of the invention as well as other objects and further features thereof, reference is read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram showing an embodiment of an electrostatic recording system;

FIG. 2 is a schematic diagram showing an embodiment of electrostatic recording mechanism of a device such as that illustrated in FIG. 1 as well as associated circuits for recording information in the form of alphabetical and numerical symbols;

FIG. 3 shows in detail an embodiment of a character of a recording wheel of FIG. 2;

FIG. 4 is a simple cross-sectional view more clearly illustrating the arrangement of elements of the instant invention; and,

FIG. 5 includes schematics and equivalent circuits comparing the instant invention to the conventional system.

Referring now to the drawings, and more particularly to FIG. 1, the electrostatic recording device comprises a suitable framework 23 and may consist of a pair of vertical side plates with rods and support means on which the working parts are mounted. The main components of the working parts are an electrostatic recording mechanism 2t) and a permanent image producing station 21. A spindle 22 at the top of the framework 23 carries a supply roll 24 of recording web material which is fed from the roll as a continuous web 25 and drawn downwardly into recording and image producing stations 20 and 21.

A controlled tension is applied to the web by sliding plate 26 which rests on top of roll 24 and whose pressure may be varied by adjusting the longitudinal position of level weight 27. The web, after traveling through recording stage 20, goes through development mechanism 28 of image producing station 21 and passes through fuser 3G. The web thereafter goes up and around web advance roller 31 and out between this roller and idler roller 32.

As the web leaves supply roll 24 it enters recording mechanism 20 wherein triggering voltages derived from digital switching system 38 are applied to suitably shaped electrodes to effect a field discharge causing a charge transfer and forming an electrostatic latent image on the Web. The operation and structure of the recording mechanism will be described in greater detail in connection with subsequent figures.

As the web proceeds downward from recording stage 20, it passes through the development mechanism 28 wherein the invisible electrostatic images are rendered visible by depositing thereon finely-divided material such as an ink mist or an electroscopic pigmented powder which adheres to the electrostatically charged image areas. To promote development, the particles are preferably charged to a polarity opposite to that of the polarity of the charge pattern by triboelectric charging or other means. A suitable powder development mechanism, for example, is shown in Patent 2,761,416, granted September 4, 1956, to Carlson, and other forms are shown and described in Carlson Patent 2,357,809 and in Walkup and Fauser Patent 2,573,881, and suitable mechanism for developing electrostatic images with an ink mist is disclosed in Carlson Patent 2,551,582.

After leaving the development mechanism, the web passes through fuser 30 wherein the resin powder devel oped image or thermoplastic web surface or both are heated in a suitable oven to a temperature suiiicient to fuse the resin. If liquid ink development is used, the fuser many serve merely as a heated drier for the ink or may dispensed with entirely. With webs formed of plastic materials, which tend to distort when heated, it is preferred that the fuser consist of a chamber filled with air saturated with vapor or solvent for the resin images and not for the web material. Solvent is absorbed by the powder until it becomes tacky or semi-tluid and as the web leaves the fuscr the solvent evaporates leaving a fused and permanent image on the web. With coated paper, the solvent for the plastic may be used, in which case it is possible to use infusible electroscopic powders as they become imbedded in the plastic or wait coating which is softened by heat or solvent as it passes through the fuser. A suitable vapor fuser is disclosed in Carlson Patent 2,776,907.

Instead of fusing the powder images on the original web, it is possible to transfer the images to another sheet or surface by an electrostatic transfer method such as is shown in Schatfert Patent 2,576,047 or by rolling against an adhesive coated surface. Thus, the resin images can be transferred and afiixed to paper offset mats for use in offset printing or multiple copies. It is to be understood that any known means for development and printing of electrostatic images may be used for this purpose.

Referring now to FIG. 2, the electrode structure of the recording mechanism and the digital switching circuit 38 for applying pulses thereto is shown in greater detail. The recording device includes a cylindrical drum 42 rotatably mounted and driven at a constant angular velocity. Circumferentially disposed at equi-spaced points about the drum are several groups of raised characters 53 of conductive material, each group constituting a ring. One ring of characters is provided for each column of recording and the cylinder extends generally across the printed page. The characters in each ring thereof are composed of the symbols A to Z and O to 9 so that both alphabetical and numerical information can be selectively recorded.

Web comprising insulating layer '71 overlying resistive layer 76 is arranged to pass with resistive layer 79 in contact with the rotating character drum. Above the web is transversely disposed an array of stationary electrodes 55, one for each ring of characters. In operation, when a selected character passes under a chosen electrode, the electrode is subjected to a trigger pulse. The triggering pulse acts to raise the stress above the critical value to produce a field discharge in the area of the character and the web and in the shape of the character, and there is formed a charge pattern having the shape of the selected character on the insulating layer 71 of web 25. l

A manner of. sequentially selecting the proper character ring and the particular character therein can involve the use of digital computer techniques as illustrated in this figure. For this purpose, mounted on the left hand side of the character drum 52 and rotating therewith is a disc 56 containing a single magnetic mark 51. A magnetic recording head 58, disposed adjacent the disc,

picks up a pulse for each revolution of the drum, which,

pulse is instantly transmitted to a revolution counter 59.

For each position of the revolution counter 59 only one of the lines marked l to N on a line selection matrix 60 is energized, the remaining lines being held at ground potential. The energized line, however, must not activate the selective electrode until the chosen character is immediately in line with electrode. The energized line is therefore connected to a gate 61 which is rendered operative only when subjected to the action of two energizing signals. 7

The second signal or energized line activates the gate only when the selected character is in line with the selected electrode. This is accomplished as follows: Magnetic marks 62 are imbedded at circumferentially spaced positions on the disc 63 attached to the right side of the drum, there being a magnetic mark for each character in the ring. These marks, which are aligned with the characters, are sensed by a magnetic head 64 disposed below disc'63 and transmitted to a character counter 65. The generation of the counting and shift pulses efiected by discs 56 and 63 may also be accomplished mechanically by toothed disc actuating suitable senor switches or other means known and conventionally used in the art.

The number in the character counter is compared in a comparison circuit 66 with the number inserted in a character register 57 by any suitable source of input digits, such as a magnetic tape system. When these two numbers agree, an output pulse is emitted by the comparison circuit es. At the moment line 5, for example, is activated by a pulse from comparison circuit as, the gate 61 under line 5 will transmit a pulse through a voltage amplifier 68 to the fifth electrode 55 thus producing a charge pattern corresponding to the selected image. After all the character images are formed, the charge patterns may be developed on the insulating layer 71 and fused, if desired, by Uhe usual method.

In the structure shown, in order to print each full line across the web, the character drum must complete as may revolutions as there are columns to be printed. If the angular velocity of the drum is made very high relative to the velocity of the web, the printed line will be substantially straight across. However, to cornpensate for any slanting or skewing which may occur in the printing, the drum may be placed at a slight angle relative to the paper or the rings may be displaced relative to each other. One such skewed arrangement is shown described in US. Patent 2,776,618 to Hartley.

It should be appreciated that for some applications a single wheel or modifications from a single rotating disc might be desirable and for further disclosure in connection with circuitry and printing in connection with such a device, the teachings of British Patent 734,909, dated August 19, 1953, are incorporated herein by reference.

A character forming element or face is illustrated in FIG. 3. In this embodiment character face 53 is shown as a raised type face. However, it is contemplated that in some instances the character faces may comprise conductive areas surrounded by insulated areas or lying in the same surface defining the edge of the wheel, or they may comprise areas of low work function material applied to a metal wheel of high work function material so that discharge will take place only from the image areas. In connection with this embodiment the various characters have been referred to as alphanumeric by which is meant a formed type or character comprising an alphabetical symbol or a numeral or the like. The characters maybe of substantially any size, and if the resulting print is of characters of a small size, improved readability can be produced by Xerographic enlargement or photographic enlargement or the images may be optically projected for reading.

To more clearly understand the arrangement of elements according to this invention, reference is had to FIG. 4. This figure shows a recording web '24, comprising insulating layer 71 overlying resistive layer '76 which is positioned in contact with character drum 42 and spaced from electrode or electrodes 55 with the insulating layer '71 facing electrode 55. After image formation at the printing gap between electrode 55' and character drum 42, web 25 is moved to developing mechanism 28 and the charge patterns on the surface of insulating layer 71 of web 25 are developed.

A possible explanation for the improvements obtained through this invention is discussed in connection with FIG. 5, but it is not intended that this theory be considered the only explanation of limitation on the mechanism of operation of this invention.

Referring now to FIG. 5, there is illustrated in FIG. 5-A a schematic of the present invention, and in FIG. 5-B a schematic of conventional electrostatic printing devices. In FIG. 5-C the circuit arrangement of FIG.

5-A is illustrated, and in FIG. 5-D the circuit arrange- V ment for FIG. 5-B is illustrated. Referring now to trode 55. In FIG. S-B the conventional arrangement is illustrated wherein character electrode 53 is spaced from web 25 while web 25 is positioned in contact with backing electrode 55. A preferred web material 25 is illustrated in FIG. 5-B and the critical material of this invention is illustrated in FIG. 5-A. This material, which is the same in both FIGS. 5-A and 5-B, comprise a layer of paper 70 or the like overcoated with an insulating plastic 71. The paper 70 may be characterized as a resistive material. In FIG. S-A the insulating coating 71 faces electrode 55 and the resistive backing 7t faces character electrode 53. In FIG. S-B insulating coating 71 faces character electrode 53 and resistive layer 70' is in contact with electrode 55.

Both the conventional technique of printing and the technique of apparatus of the instant invention have been employed using a film of insulating material without any resistive layer. However, in order to produce quality images useful in commerce, it has been found necessary to use a resistive backed layer in the instant invention, and it has been found desirable to position the resistive portion against the image defining electrode which, as illustrated in FIG. 4, requires the developing mechanism to be positioned to develop the insulating portion of web 25. One advantage is that, if a purely insulating material is employed, the rubbing of the insulating material as it moves relative to and against electrode 53, which generally is of a different material, produces static changes along the web which are developed during the developing procedure, thus creating spurious and uncontrolled deposit of particles and poor quality developed images. This problem is somewhat overcome by the use of a relatively conductive layer 70 in contact with electrode 53 since any charges which deposit through the rubbing contact of the web 25 with electrode 53 are dispersed through the conductive layer prior to the developing operation and thus do not develop out.

Although layer 76 has been referred to as resistive or conductive, a critical value of conductivity or resistivity is required in connection with this invention. In particular, this layer cannot be a pure conductor so that it acts as a shield which prevents the creation of the desidered field and electrostatic image formation in accordance with the concepts of field discharge involved herein. In fact, it must be sufiiciently resistive to act substantially as an insulator during the time of pulsing or during the time of image formation. Thus, its relaxation time should be sufficiently great to prevent resistive layer 70 from acting as a shield during image formation. Following image formation, this layer should be sufiiciently conductive to allow dissipation of any spurious charges deposited during the moving contact between web 25 and electrode 53. Typically, paper has been used as a medium having these desired characteristics and hence can be characterized as a charge dissipating layer. Generally, the paper is treated to have a 3% water content at the time of manufacture and then wrapped in a waterproof container so that at the time of use it still has this content. It is believed that this water content is equivalent to paper allowed to absorb moisture from the air under normal humidity conditions generally above about 40% relative humidity. Obviously, the necessary resistivity of the paper is dependent on the time constant or width of the pulse applied between the electrodes. As an example of a Working arrangement, when using a 1500 volt pulse it has been found that the paper just described is operable within the scope of this invention using a pulse width between about 2 microseconds to about 1 second. It is noted however, that the results in this range are nonlinear in that results up to about 400 microseconds seem about the same. Then between about milliseconds to about 100 milliseconds results are poor. They improve between about 215 milliseconds through about 1 second.

b This same paper has also operated with different voltages, and its resistivity has been measured as 4x10 ohm centimeters in a room having a relative humidity of 17% using a Hart Moisture Meter, type K-103, manufactured by Bart Moisture Meters, 336 West Islop Boulevard, West Islip, New York.

The electrical circuits in FIG. 5-C and 5-D include a comparison for a point on the coated paper in image areas and a point on the paper in fringe areas. Points 1 and F are such points respectively and are included in FIGS. 5-A, B, C and D. This distinction has been made since improved resolution is characteristic of images formed according to this invention as compared to conventional image formation, and an analysis of the circuit differences suggest a possible reason for the improved results.

Considering further FIGS. 5-0 and 5-D, improved resoiution may be explained by circuit differences. The elements include C as the capacity of the paper coating, C as the capacity from the surface of the paper directly to the electrode. C is considerably larger than C which is the capacity from the fringe point to the character electrode. R is the resistance directly through the thickness of the paper while R is the much larger resistance from a point in the fringe area to the character electrode. In FIG. 5-C one element is different in the two branches of the circuit and in FIG. 5-D one element is different in the two branches of the circuit. It is now believed that the difference between printed or non-printed edge areas or electrostatic image resolution of the image may be determined by the diiference between R;, and R in the case of this invention, and between C and C in the case of conventional electrostatic printout systems. As should be apparent in both cases, this results in a difference in the electric field strength at the image and fringe points. In the conventional system the resolution depends on the magnitude of the C /C ratio. This ratio is large at small gaps and such gaps are used to form images through electrostatic discharge phenomenon. In fact, experience has shown that the best conventional images are made with as small a gap as the mechanical and electrical characteristics of the system permit. However, excessively small gaps hinder electrical discharge and create serious practical mechanical problems. Where the gap is made vary small, it becomes increasingly difficult to maintain the gap uniform. According to this invention, however, resolution depends on the magnitude of the R /R ratio. This ratio can be made very large simply by employing a thin paper layer, and generally the resistive layer is smaller than the gap of the conventional system. A thin paper layer does not impede electrical discharge and does not call for any higher degree of mechanical perfection in the system.

Further, the distinction between resistive and capacitive ratios may play some part in producing images of better resolution.

In the embodiment illustrated in FIG. 2 and FIG. 4 using characters of the type illustrated in FIG. 3, the drum or" characters rotates at a much higher linear speed than does the web material. The first reaction one has is that the web material would be abraded beyond repair by the rapidly rotating drum. However, it has been found that there is no adverse efiect on print quality or on the web material brought about by the rapid rotation of the drum in contact with the web material. The web material has been wrapped about the drum over an arc of about 70 degrees and has been subjected to drum speeds of 12,000 revolutions per minute with the web material moving extremely slowly or standing stationary. Very slight burnishing occurs in areas of the columns. However, the paper did not become abraded. Experiments were also conducted using character drums having plastic filling material in order to present a smooth surface. The resalts were substantially the same as those including raised characters.

Various gaps have een included between the backing electrode and the web material. With air in the gap, a gap of about 4 r mils and a pulse amplitude of about 900 volts has been found optimum for highest quality printing. It has also been found that an increase or decrease in gap requires a commensurate increase or decrease in voltage of about 160 volts per mil change. Generally, however, it is preferred to operate above about 3 mils of air gap. Typically, when employing a gap of 3 mils or less, images including halos are formed and partial rather than complete characters frequently form. As the gap increases above about mils, image resolution as well as image contrast decreases in quality rapidly. Thus, the preferred range is generally between about 3 to about 10 mils.

In practice, the drum has been rotated at'12,(l )i) revolutions per minute and generally a DC. bias voltage is applied to the backing electrode in respect to the character drum. This bias voltage is to apply part of the potential necessary for breakdown but an insufficient amount of potential to break down the gap. This simplifies the pulse equirements for image formation. in effect, if the threshold pointis 660 volts and 550 volts are applied to a bias potential, then only about a SO-volt pulse is necessary to break down the gap. In practice 600 to 900 volts more than the breakdown voltage is used for image formation. Thus, in the example given, a pulse of about 650 volts would be applied to print. The web speed which is generally preferred is about 60 inches per minute, but also it'is preferred that variable speeds be provided for, so

that the web may be moved, for example, between about 30 to 90 inches per minute. With the drum rotating at high rates of speed, ionization and image formation must take place in a very short time to prevent blurring or smearing of the formed charge pattern. With a gap of about 4 to 5 mils between the web and the backing electrode with a drum rotating at about 12,080 revolutions per minute, and using a web material of cellulose acetate butyrate-coated paper having a total thickness of about 3 mils, a pulse of about 6G0 to 900 volts for about 3 microseconds duration including a bias anywhere from 600 to 1100 volts and a pulse width of between about 2 to microseconds, and preferably between about 2 to 10 microseconds, has produced extremely high quality images. The drum which was used was an aluminum drum with rings of steel characters.

T16 terms field discharge as used throughout is intended to mean a field induced silent electric discharge between the character forming elements and the backing electrode including interposed therebetween an insulating layer resulting in the formation of an electrostatic charge pattern on the insulating layer corresponding to the shape of the discharge. This type of discharge is not like a spark discharge, but creates a conductive gap whereby charges how for deposition to the insulating surface. Generally, can be considered a cold discharge, and generally also, image formation occurs in the absence of other phenomenon such as thermionic emission. Also, in forming images according to this invention, it is not intended to mean image formation through chemical or physical changes in the recording web. The specific nature of the discharge is dependent on various'elements and factors such as the potentials, the field strength, the electrode materials, the fluid of the gap, wl'lether air or other gas or liquid, the pressure and the like. For more discussion of this type of discharge, reference may be had to issued patents in this art. 7

Although particular embodiments of the invention are shown in the drawings and described in the foregoing specification it will be understood that invention is not limited to those specific embodiments described but is capable of modification and rearrangement and substitution of parts and elements without eparting from the spirit of the invention.

What is claimed is:

l. A device for recording electrostatic images which comprises in combination, a conductive electrode, a conductive alphanumeric character face and means to support said character face in closely spaced facing relationship with the surface of said electrode, means to position a sheet material having an insulating surface layer overlying a charge dissipating layer between said character face and said electrode with said charge dissipating layer in contact with said character face and with said insulating layer facing and spaced from said electrode and means to apply an intense electric field between said character face and said electrode to produce a silent field discharge conforming in configuration to said character face to produce an alphanumeric electrostatic latent image on said insulating surface.

2. A device for recording electrostatic images at atm0spheric pressure which comprises, in combination, a conductive electrode, a plurality of conductive alphanumeric character faces and movable support means therefor to bring said character faces into closely spaced relationship with said electrode, means to advance a sheet material having an insulating surface layer overlying a charge dissipating layer between said electrode and said characterfaces with said charge dissipating layer in contact with said character faces and with said insulating layer facing and spaced from said electrode, and means to create an intense electric held between said electrode and said closely spaced character faces to create a field discharge conforming in configuration with said character faces creating on said insulating surface an invisible electrostatic charge pattern conforming to said character faces.

3. A device for rapid recording of electrostatic images which comprise, in combination, a wheel carrying a series of conductive alphanumeric character faces on the periphery thereof, a stationary conductive electrode mounted in closely spaced relationship to a portion of the periphery of said wheel, means to advance a sheet material having an insulating surface layer overlying a charge dissipating layer between said electrode and said wheel with said charge dissipating layer in contact with said wheel and with said insulating layer facing and spaced from said electrode, means to rotate said wheel around its axis, means to apply an intense field discharge generating electric field of short duration between said electrode and a selected character on said wheel at the instant said character is passing a predetermined position in front of said electrode thereby forming on said sheet material an electrostatic latent image conforming in configuration with said selected character, and means to develop the insulatmg layer following image formation thereon.

4. A device to record alphanumeric information on a moving web from a signal source, said device comprising an electrostatic printing station and means to advance a web comprising an insulating layer overlying a charge dissipatmg backing past the printing station, an electrode positioned adjacent to said web across the direction of motion thereofla series of electrostatic printing means in combination with said electrode, each printing means comprising a conductive alphanumeric character face positioned on a movable support means in sequence to bring character faces of the printing means successively into closely spaced relationship with said electrode to form electrode character combinations in timed relationship, means to receive the advancing web of insulating material between saidelectrode character combinations with said charge dissipating portion against said electrostatic printmg means and said insulating layer facing and spaced from said electrode, means to energize said electrode character combinations through said web and successively across the direction of motion of the web, and means 7 sequentially coordinated in time relationwith successive signal voltages of said signal source to activate said character electrode combinationssuccessively to apply silent discharge voltage pulses between the electrode and the 9 character faces whereby an electrostatic charge pattern corresponding to said character faces is placed on the insulating layer of said web in response to said signal source.

5. Electrostatic apparatus for recording information comprising a rotary character drum provided with a pinrality of circumferentially arranged character shaped electrodes, means to move a web comprising an insulating layer overlying a charge dissipating backing in physical contact with and relative to said drum, another electrode mounted to cooperate with said drum and positioned to allow passage of said web between said electrode and said drum with said insulating portion of said web facing and spaced from said other electrode, means to apply an electric potential difference between the character shaped electrodes and said other electrode to produce an electric field between the character faces and said other electrode which is below the threshold potential at which field discharge starts, and means to apply a triggering pulse of potential difference between said other electrode and a selected character on said drum when said character is positioned adjacent to said web, said triggering pulse having an intensity sufficient to effect an electric field discharge whereby an electrostatic latent image of said selected character is formed on said insulating layer of said web.

6. A device for recording at atmospheric pressure comprising an information converter comprising a multiplicity of conductive elements, a conductive electrode, means to move a Web comprising an insulating layer overlying a charge dissipating layer relative to and with said charge dissipating layer in physical contact with said information converter while between said information converter and said conductive electrode and with said insulating layer of said Web facing and spaced from said conductive electrode, said conductive elements of said converter being positioned and adapted to form through electrical field discharge a two-dimensional invisible electrostatic image on said insulating layer, means to create an electric field between said selected elements of said converter and said electrode in accordance with inforfation to be recorded, said field being of suficient intensity to create a silent discharge in conformity with the information fed to said converter to be recorded producing a two-dimensional electrostatic charge pattern on said insulating layer conforming to said information.

7. A device for recording electrostatic images which comprises, in combination, a rotatable character drum having a bank of like character rings thereon, each ring containing a series of electrically conductive character shaped elements in a circumferential arrangement, the respective characters in the series being representative of different values of incoming information, conductive electrodes positioned adjacent to and facing each character ring of said character drum, means to rotate said drum at a constant velocity, a movable web comprising an insulating layer overlying a charge dissipating backing disposed relative to said drum and with said charge dissipating backing in contact with said drum and said insulating layer facing and spaced from said electrodes, and means responsive to the value of incoming information to apply a voltage pulse to one of said electrodes when the ring element representative of said value is in angular alignment with said electrode to create an intense electric field between said electrode and said ring element to create field discharge forming a latent electrostatic image of the selected character on said insulating layer on said web.

8. Apparatus according to claim 7 including means to sequentially apply voltage pulses to said electrodes and to shift said pulses to the next electrode after each recording operation.

9. Apparatus according to claim 7 including line storage memory means and simultaneous selective pulsing 10 means to produce line at a time electrostatic image formation printing on said insulating layer.

10. Apparatus according to claim 7 in which said character carrying drum is rotated at a speed up to about 12,000 revolutions per minute and in which said web material is moved at a speed of about 30 to inches per minute.

11. Apparatus according to claim 10 in which said bias pulse to produce discharge and image formation is applied for about three microseconds.

12. In the method of tesiprinting on an insulating surface which includes bringing an alphanumeric conductive character into closely spaced relationship with a conductive electrode, positioning a recording web between said character and said electrode and applying an intense electric field between said character and said elec trode to produce field discharge and electrostatic image formation on said web, the improvement comprising employing a web comprising an insulating coating overlying a charge dissigating support layer and positioning said web with said charge dissipating layer in physical contact with said character face and said insulating layer spaced from said conductive electrode.

13. The method of electrostatic recording in air at atmospheric pressure which comprises bringing a conductive shaped character face on a support therefor into substantially parallel relationship with a facing conductive electrode, positioning a recording web comprising an insulating surface coating on a paper layer between said character face and said electrode with said paper layer in physical contact and facing said character face and with said insulating layer facing and spaced by a gap of between about 3 to 10 mils from said electrode, and producing an electric field between said character face and said electrode suflicient to produce field discharge to form an electrostatic charge pattern corresponding to said character face on said Web.

14. The method of claim 13 in which the voltage to produce field discharge is applied for a time between about 2 microseconds to about 1 second.

15. The'method of recording which comprises advancing a recording web comprising an insulating layer overlying a charge dissipating backing parallel to its surface and past a multiplicity of conductive elements, said conductive elements being positioned and adapted relative to said recording web to form through electrical field discharge a two-dimensional invisible electrostatic image on said web as said web moves relative thereto, said web being positioned with said charge dissipating backing in physical contact with said multiplicity of conductive elements, applying a short voltage pulse between selected elements of said multiplicity and an electrode positioned facing said insulating layer of said web in accordance with information to be recorded and of sufiicient intensity to create a sufiicient electric field to create a silent discharge in conformity with the information to be recorded producing a two-dimensional electrostatic charge pattern on said recording web while maintaining the original physical and chemical characteristics of said web.

16. The method of recording images which comprises bringing an electrode having an alphanumeric conductive character face into closely spaced relation with a conductive second electrode, positioning a recording web comprising an insulating coating overlying a charge dissipating backing between said electrodes and with said charge dissipating backing in contact with said character face electrode and with said insulating coating facing and spaced from said second electrode, and applying an intense electric field between said electrodes to produce a cold field discharge between said electrodes resulting in the formation of an electrostatic image conforming to said alphanumeric character face on said recording web.

17. The method of recording which comprises advancing a recording Web comprising an insulating coating overlying a charge dissipating backing parallel to its surface, simultaneously moving a series of shaped conductive characters in a closed path which brings each of said characters successively into closely spaced face-toface relationship with a conductive electrode, moving said recording web between said character-electrode combinations with said charge dissipating backing in physical contact with said conductive characters and said insulating coating facing-said conductive electrode, and applying a short voltage pulse between a selected character and said conductive electrode when said character is in said closely spaced face-to-face relationship with said electrode, said pulse being of sufiicient amplitude to form an electrostatic image corresponding to said character on said recording Web and of a short enough duration relative to the speed of motion of said Web to maintain distinctness in the image on said web while the original physical and chemical characteristics of said recording web are maintained.

18. A device for recording electrostatic images which comprises in combination, a conductive electrode, a conductive alphanumeric character face and means to support said character face in closely spaced facing relationship with the surface of said electrode, means to position a sheet material having an insulating surface layer overlying a charge dissipating layer between said character face and said electrode with said charge dissipating layer facing said character face and with said insulating layer facing and spaced from said electrode and means to apply an intense electric field between said character face and said electrode to produce a silent field discharge conforming in configuration to said character face to produce an alphanumeric electrostatic latent image on said insulating surface.

19. A device for recording at atmospheric pressure comprising an information converter comprising a multiplicity of conductive elements, a conductive electrode, means to move a web comprising an insulating layer overlying a charge dissipating layer relative to and with said charge dissipating layer facing said information converter while between said information converter and said conductive electrode and with said insulating layer of said web facing and spaced from said conductive electrode, said conductive elements of said converter being positioned and adapted to form through electrical field discharge a two-dimensional invisible electrostatic image on said insulating layer, means to create an electric field between said selected elements of said converter and said electrode in accordance with information to be recorded, said field being of sufficient intensity to create a silent discharge in conformity with the information fed to said converter to be recorded producing a two-dimensional electrostatic charge pattern on said insulating layer conforming to said information.

References Qited by the Examiner UNlTED STATES PATENTS 2,883,257 4/59 Wehe 346-74 2,919,171 12/59 Epstein et al 346-74 2,919,967 1/60 SchWertZ 34'6-74 2,932,690 4/60 Adams et al 346-74 3,060,432 10/62 Schwertz 346-74- OTHER REFERENCES Standard Handbook for Electrical Engineers, ninth' 

4. A DEVICE TO RECORD ALPHANUMERIC INFORMATION ON A MOVING WEB FROM A SIGNAL SOURCE, SAID DEVICE COMPRISING AN ELECTROSTATIC PRINTING STATION AND MEANS TO ADVANCE A WEB COMPRISING AN INSULATING LAYER OVERLYING A CHARGE DISSIPATING BACKING PAST THE PRINTING STATION, AN ELECTRODE POSITIONED ADJACENT TO SAID WEB ACROSS THE DIRECTION OF MOTION THEREOF, A SERIES OF ELECTROSTATIC PRINTING MEANS IN COMBINATION WITH SAID ELECTRODE, EACH PRINTING MEANS COMPRISING A CONDUCTIVE ALPHANUMERIC CHARACTER FACE POSITIONED ON A MOVABLE SUPPORT MEANS IN SEQUENCE TO BRING CHARACTER FACES OF THE PRINTING MEANS SUCCESSIVELY INTO CLOSELY SPACED RELATIONSHIP WITH SAID ELECTRODE TO FORM ELECTRODE CHARACTER COMBINATIONS IN TIMED RELATIONSHIP, MEANS TO RECEIVE THE ADVANCING WEB OF INSULATING MATERIAL BETWEEN SAID ELECTRODE CHARACTER COMBINATIONS WITH SAID CHARGE DISSIPATING PORTION AGAINST SAID ELECTROSTATIC PRINTING MEANS AND SAID INSULATING LAYER FACING AND SPACED FROM SAID ELECTRODE, MEANS TO ENERGIZE SAID ELECTRODE CHARACTER COMBINATIONS THROUGH SAID WEB AND SUCCESSIVELY ACROSS THE DIRECTION OF MOTION OF THE WEB, AND MEANS SEQUENTIALLY COORDINATED IN TIME RELATION WITH SUCCESSIVE SIGNAL VOLTAGES OF SAID SIGNAL SOURCE TO ACTIVATE SAID CHARACTER ELECTRODE COMBINATIONS SUCCESSIVELY TO APPLY SILENT DISCHARGE VOLTAGE PULSES BETWEEN THE ELECTRODE AND THE CHARACTER FACES WHEREBY AN ELECTROSTATIC CHARGE PATTERN CORRESPONDING TO SAID CHARACTER FACES IS PLACED ON THE INSULATING LAYER OF SAID WEB IN RESPONSE TO SAID SIGNAL SOURCE. 